Rigid, wedge-shaped mounting structure for minimizing resonances to allow rapid transverse movement of an attached head

ABSTRACT

An improved head mounting assembly includes a wedge-shaped rigid head support member which minimizes resonances when operating at rapid transverse head movements, and which operates in conjunction with a photo-sensitive head positioning apparatus, to provide improved tracking for a transducing head mounted on the member.

FIELD OF THE INVENTION

This invention relates to an improved mounting assembly for a magnetictransducing head, the mounting assembly permitting rapid and preciselyrepetitive lateral displacement of the head in a direction transverse tothe recorded track provided on a magnetic tape, thus permitting the headto follow the recorded track more accurately.

BACKGROUND OF THE INVENTION

In the prior art the transducing head is mounted on a flexiblelongitudinal leaf member, the leaf member mounted as a cantilever beam,secured at one end to a mounting base to extend outwardly from the baseand support a transducing head at the free end of the beam. In thehelical-scan magnetic tape transport art, one or more of these leaf-typemembers may be used, each mounted at the interior of a rotating drum, toextend radially toward the periphery of the drum, the head protrudingthrough an opening in the drum to traverse or scan the recorded trackson a magnetic tape curved around the periphery of the drum in a helicalpath.

A mounting arrangement as described above typically incorporates amechanism for driving the leaf member, such as a voice coil assemblyinteractive with the leaf member for positioning the head by means of afeedback circuit connected between a head positioning apparatus and thevoice coil assembly. However, a significant disadvantage of such a headpositioning arrangement is the limitation of head positioning parametersto relatively low speed displacements, since the relatively long andthin head positioning member will not uniformly bend at high speeds.That is, the inherent flexibility of the long, thin head positioningmember sets up undesirable resonances in the member under rapid andrepetitive flexure loadings. Such resonances also result in undesirablechanges in the bending moment under repeated flexures of such member.The occurrence of such conditions in the member under the desiredloading sequence severely impairs the ability of a head mounted on themember to follow a tape track recorded on a magnetic tape.

One prior art support structure for a transducing head is shown in U.S.Pat. No. 4,212,043 by Baker entitled "Magnetic Transducing", issued Jul.8, 1980 and assigned to the assignee of the present invention.

However, that patent, although displaying a more stable structurepresents a structure which is directed to controlling the movement of ahead stack having multiple heads disposed adjacent a magnetic tape. Themovement of a head stack has to be parallel to the plane of the tape toenable each head in the stack to follow a respective track on the tape.A single head mounted on a leaf member is positioned to engage a singletape track, and positioning of that single head by a cantilever bendingelement is viable because of the relatively small displacementsinvolved. Further, the patented structure is also directed to solvecertain problems introduced by centrifugal forces bearing against thesupport structure and not problems relating to rapid and repetitivedisplacement of the transducing heads. Moreover, the structure of thedevice described in the aforementioned patent is not amenable to theswift and repeated displacements required in a system directed to therapid processing of data, i.e., a digital tape transport.

SUMMARY OF THE INVENTION

Accordingly, the mounting assembly of the present invention is directedto an apparatus and method for use in a magnetic recording system whichrequires rapid and repetitive positional changes of the transducing headwith respect to the data tracks, such transducer mounting assemblyrequiring a bending member of light-weight construction, but havingsufficient rigidity along the major portion of its length to minimizechanges in the bending moment under rapid changes in head position Thepresent invention produces a more stable structure and an improved RFoutput at the head Moreover the present invention includes an improvedbending structure which aligns the head with the neutral plane of thebending element associated with the mounting structure Alternativeconfigurations are also shown. A photo-cell arrangement associated withthe head positioning apparatus is responsive to small changes in headposition to precisely drive a voice coil motor associated with saidapparatus.

Accordingly, the transducer mounting assembly of the present inventionincorporates a longitudinal head support member structured to provide alight-weight, but substantially rigid, longitudinal main body portion ofwedge-like shape and including a relatively short, simple hinge flexureextending from the rigid main body portion and secured to a base. Toaccomplish a lightweight but rigid construction, the head support memberis formed from a single thin sheet of a light weight metal, i.e.,stamped aluminum, and folded into a hollow outer frame having awedge-like shape of a form which maximizes the rigidity of the member.To maximize head contact with the tape during deflection, the headmounting portion of the outer end of the rigid member is so positionedas to align the longitudinal mid-plane of the track width associatedwith the head with the horizontal neutral plane of the rigid member.Moreover the assembly of the present invention incorporates an improvedhead positioning apparatus for the head mounting assembly, said headpositioning apparatus including a photo-cell arrangement which respondsquickly and precisely to relatively small changes in head position tosupply head positioning information to a voice coil drive motorpositioned on the mounting assembly to drive and position the memberwith speed and accuracy under rapid and repetitive displacement of thetransducing heads.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of the head mounting assembly of the presentinvention taken along the lines 1--1 of FIG. 2;

FIG. 2 is a top plan view of the head mounting assembly of FIG. 1 withportions removed for clarity;

FIG. 3A is a top plan view of the head support member of FIG. 1;

FIG. 3B is a sectional view taken along the lines B--B of FIG. 3A;

FIG. 3C is a front elevation taken along the lines C--C of FIG. 3B;

FIG. 4 is a top plan view of the blank from head support member isformed;

FIG. 5 is a top plan view of the head clamp assembly of the headmounting assembly shown in FIG. 1;

FIG. 6 is a schematic illustration of a magnetic tape and a tape trackthereon;

FIG. 7 is a schematic diagram of a circuit designed to control the tapetracking of a head mounted on the support member;

FIG. 8 is a schematic representation of a portion of the head mountingstructure of a first embodiment of the present invention, showing aouter end of a longitudinal member of the structure, and the position ofa transducing head with respect thereto, the head so mounted on saidmember as to dispose a mid-plane of the track width defined by the heada small distance below the horizontal neutral plane of said member;

FIG. 9A is a schematic representation of a portion of a secondembodiment of the improved head mounting structure of the presentinvention, wherein the outer end of a longitudinal member of thestructure is tilted upwardly to position a longitudinal mid-plane of thetrack-width as defined by the head in alignment with the horizontalneutral plane of the member;

FIG. 9B is a schematic representation of a portion of a third embodimentof the improved head mounting structure of the present invention,wherein the outer end of a longitudinal member of the structure istilted downwardly to position a longitudinal mid-plane of the trackwidth as defined by the head in alignment with the horizontal neutralplane of the member;

FIG. 9C is a schematic representation of a portion of a fourthembodiment of the improved head mounting structure of the presentinvention, wherein the outer end of a longitudinal member of thestructure has an upwardly directed notch provided therein, whereby thehead is positioned in the notch so as to align a longitudinal mid-planeof the track width as defined by the head with a primary horizontalneutral plane of the member;

FIG. 9D is a schematic representation of a portion of a fifth embodimentof the improved head mounting structure of the present invention,wherein the outer end of a longitudinal member of the structure receivesa head support member which also engages the head to align alongitudinal mid-plane of the track width as defined by the head withthe horizontal neutral plane of the member;

FIG. 9E is a schematic representation of a portion of a sixth embodimentof the improved head mounting structure of the present invention,wherein the outer end of a longitudinal member of the structure engagesa notch provided at the rear of the head to align a longitudinalmid-plane of the track width as defined by the head with the horizontalneutral plane of the member; and

FIG. 10 is a graph which compares head tip penetration across the entirehead deflection range for the current structure, the proposed structure,and a modification of the proposed structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1 and 2, embodiment one of a head mounting assembly 10disposed in a scanner (not shown), comprises a base 11, mounted on abase plate 12, and a transducer or head support member 14, including anelongated, wedge-shaped frame or main body portion 16 and a pair ofhinges 18 extending from one end of the member 14 to engage a clampingmember 20 of the base 11. A head clamp assembly 22 is disposed at theend of the support member 14 opposite the hinges 18 to support atransducer position sensing apparatus 26. Underlying the clamp assembly22 is a voice coil mechanism 27, disposed adjacent the base 11, andincluding a motor support 28 and a voice coil motor 29. The motor 29 isdisposed to receive a complementary coil element 30 mounted on thebottom of the support member 14 adjacent the position sensing apparatus26, in a cylindrical gap 31 provided in the motor 29 and aligned withthe element 30. The motor 29 operates in conjunction with thepositioning apparatus 26, through circuitry described below, to positiona head 24, mounted at the end of the member 14 opposite the hinges 18.The voice coil mechanism 27 rests on the base plate 12, which is thebottom plate 12 of the rotating upper drum (not shown) of the scanner.

Of particular interest in the present invention is the form andstructure of the wedge-shaped head support member 14, such structurebetter seen in FIGS. 3 and 4. The member 14 is formed as an outer frame16 from a single, flat, sheet-like element 32, as shown in FIG. 4. Thesheet 32 may be formed from any suitable light-weight material, but itis preferable that the material is thin, flexible and easily etched;e.g., thin sheet aluminum. The flat sheet 32 is struck in a complex formwhich is generally concentric about a center line 32a and includes ahead support structure 34 at the front and a pair of flat, flexiblehinges 18 at the rear. Holes 38, 39 are etched in the sheet 32. Theholes 38 are all of a relatively similar size and form such lineararrays as 38a and 38b to provide fold lines for use in forming the sheet32 into the rigid, wedge-shaped, beam-like frame 16 of the member 14.The holes 39, of varying sizes, serve only to reduce the weight of theframe 16 at those points on the sheet 32 where the removal of materialwill not affect the rigidity of the frame 16.

Moving from the bottom of the sheet 32 in FIG. 4, and upward toward thecenter line 32a, the main body portion 40 of the member 32 not onlyincludes the fold lines 38a and 38b, but also fold lines 38c and 38d.Corresponding fold lines 38a', b', c' and d' are shown on the upper halfof the member 32. To orient the sheet 32 with the structure of the headsupport member 14, the fold lines 38a-38d and 38a40 -38d' are also shownin FIGS. 3A-C, with the sheet 32 being folded upwardly and outwardlyfrom the plane of the paper as shown in FIG. 4, to dispose respectiveside walls 41 and 41' between fold lines 38a, b and 38a', b'. When thesheet 32 is folded, a flap 42 with outwardly extending ears 42a, atopposite ends thereof, is carried inwardly to first pivot about the foldline 38a to dispose the flap 42 concentrically about the center line32a, with a respective ear 42a folded to engage each of the side walls41, 41'. A flap 41a', on side wall 41' is tucked under an upperextension 42c of the flap 42, adjacent the fold line 42b. The headsupport structure 34 comprises a generally U-shaped forward extension ofthe sheet 32 including leg portions 34a, which are folded rearwardlyabout a fold line 34b to engage the flap 42 pivoted about the fold line42b, the flap 42 folded sufficiently to dispose the flap 42perpendicular to the base of member 14, with the ends 34a of theextension 34 overlying flap 42 at an upper end thereof, with the members34, 42 thereafter to be held in place as by welds 44. Also providedwithin the flap 42 is a head window 46.

The completed member 14, as shown in FIGS. 3A-C, comprises an openframework of longitudinal elements which form a substantially rigid, butlightweight wedge-shaped, beam-like structure sufficiently rigid tominimize changes in its bending moment under rapid changes in headposition. From the truncated triangular base 16a, of main body portion16, to a similar triangular structure in both outer walls 41, 41' andinner walls 43, 43', a substantial design effort was undertaken tominimize weight, maximize rigidity and eliminate undesirable resonancesin order to achieve an optimum weight-to-strength ratio.

As shown in FIGS. 1 and 2, the member 14 is mounted in the base 12 withthe hinges 18 held in place in the clamping member 20 on opposite sidesof the center line 32a by fasteners 47. A relatively small area offlexure 36 is provided in each hinge 18 between the main body portion 16of the member 14 and the base 11. The voice coil mechanism 27 underliesthe head support member 14 in the area of the window 46. Connectors 53connect the voice coil element 30 on the support member 14 to terminals54 provided on the base 11. Overlying the voice coil motor 29 is thehead clamp assembly 22.

As seen in FIG. 1, the head clamp assembly 22 comprises a main bodyportion 55, secured to the base 11 by a fastener 56. Mounted in the mainbody portion 55 forward of fastener 56 is the position sensing apparatus26, comprising a light emitting diode (LED) 58 and upper and lowerphoto-voltaic light sensing cells 59, 60. The position sensing apparatus26 is so disposed in the main body portion 55 that when the assembly 22is mounted on the base 11 to overlie the member 14, the LED 58 is placedon one side of the window 46 in the member 14 and the photocells 59, 60are placed on the opposite side. Circuit elements 61 connected to thelight emitting diode 58 and circuit elements 62 connected to thephotocells 59, 60 are in turn connected to conductive posts 63 and 64respectively. The posts 63, 64 are interconnected to a servo circuit 66interacting with the voice coil motor 29 to position the transducer orhead 24 mounted at the outer end of the head support member 14.

As the voice coil motor 29 moves the member 14 and the head 24, theamount of light falling on each of the photocells 59, 60 varies as afunction of position. That variance is converted to an electrical signalof a magnitude defined by the difference in the amount of light receivedby the cells 59, 60 in the circuit 66 (FIG. 7) and thereafter used bythe circuit 66 to position the head 24 on a tape track.

In FIG. 6 a section of magnetic video tape 68 is schematically shownwith one track 69 of data (depicted in a dashed line) previouslyrecorded by a helical scan video tape recorder. As previously mentioned,during data recording and reproducing operations, the tape is guidedunder tension so that recording occurs under a recommended standardvalue of longitudinal tension, which induces a certain degree ofstretching of the tape. If the tape is played back at a differenttension because of faults in the tensioning mechanism, or because ofunavoidable variations in the mechanisms of different machines, then thelength, straightness and inclination of the data relative to the videohead track will be different. Under such circumstances, the head willnot perfectly follow the data track, leading to undesirable variationsin the strength of the reproduced signal such as variations in theamplitude of the RF envelope 70. A similar effect results if the correcttension is used on playback, but the tape has shrunk or elongated due tochanges in atmospheric or storage conditions, e.g., temperature orhumidity. Also, irregular tape edges and differences in edge-guidingeffects from machine to machine, can cause irregularly wandering tracksor scans. Consequently the path 71 taken by the video head 24 duringreproduction as it scans the tape 68 often fails to exactly coincidewith the recorded track 69. In actual practice it has been found thateven slight deviations between the recorded track 69 and the path 71taken by the reproduce head 24 can result in significant deteriorationin the quality of the reproduced video signal.

Accordingly, to minimize the deviations noted above between the recordedtrack and the path 71 taken by the reproduced head 24, the structure ofthe present invention has been further modified to assure that themovement of the member 16 corresponds more exactly to the movement ofthe head 24. For example, in FIG. 8, the outer end 16a of the member 16carries the transducer or head 24 below the end 16a, disposing alongitudinal mid-plane 25 of the head 24 below a plane defining thelower face 16c of the member 16 and therefore below a neutral plane 16bwhich is co-extensive along the member 16 with the mid-plane of thehinge. Because the bending axis associated with head deflection is moreprecisely a series of bending axes whose radii decrease as thedeflection of the member 16 increases, it is desirable to align thetrack associated with the head with the horizontal neutral plane of themember so as to minimize asymmetries occurring across the deflectionrange of the head, particularly since such asymmetries diminish thequality of head output.

In a second embodiment of the present invention, which uses the mountingstructure shown in FIGS. 1-5, and is shown FIG. 9A, to align alongitudinal mid-plane 125 of a transducer or head 124 with a horizontalneutral plane 116b (the plane co-extensive with the mid-plane of thehinge) of a member 114 the member 114 was modified to provide a tiltedouter end 114a, the outer end 116a of the member 114 tilted upwardly toaccommodate the transducing head 124 at the bottom thereof. The desiredconfiguration mutually aligns the horizontal neutral plane 114b of themember 114 with a longitudinal mid-plane 125 associated with the trackwidth of a track generated by the head 124. With the neutral plane 114bof the member 114 aligned with a longitudinal mid-plane 125 of the trackwidth defined by the transducer 124, distortion of the RF envelopeduring deflection of the head 124 is minimized.

In FIG. 9B, a third embodiment of the head support structure describedabove is shown, wherein an outer end 214a of member 214 is tilted downdownwardly to accommodate engagement of a transducing head 224therewith, and a mid-plane 225, associated with a track width generatedby the transducing head 224, is aligned with a neutral plane 214b of themember 214.

A fourth embodiment of the head support structure is shown in FIG. 9Cwherein an outer end 314a of a member 314 includes a lower notch 317 sopositioned as to engage a transducing head 324 to align the longitudinalmid-plane 325 associated with its track width with a neutral plane 314bof the member 314.

A fifth embodiment is shown in FIG. 9D wherein a head mounting plate 418is disposed at an outer end 414d of a member 414 and displacedsufficiently below the outer end 414a so that a transducing head 424 canbe mounted thereon, with the longitudinal mid-plane 425 associated withits track width aligned with a neutral plane 414b of the member 414.

A sixth embodiment of the present invention is shown in FIG. 9E whereina notch 526 is provided at a rear face 527 of a transducer 524. In theembodiment of FIG. 9E an outer end 514a of a member 514 is received inthe notch 526 to align a neutral plane 514b of the member 514 with alongitudinal mid-plane 525 associated with the track width of head 524.

Each of the embodiments shown is to dispose the mid-plane of the trackwidth as defined by and associated with the head 24 in alignment withthe horizontal neutral plane 14b of the member 16. In FIG. 10 each curverepresents a tip projection differential achieved during the deflectioncycle, over the entire range of deflection. When the head is displacedfrom the neutral plane, as in the 13 mil offset curve, there is asubstantial difference in tip penetration differential at opposite endsof the range, from -400 micro inches at end of the range to +70 microinches at the opposite end. Such a configuration results in substantialdistortion of the RF envelope, and a loss in picture quality.

More favorable tip projection profiles are achieved with a zero (0)offset curve. With a zero offset it can be readily seen that tippenetration falls within range of a -120 to -150 micro inches atrespective opposite ends of the range, eliminating asymmetries in thecurve, and thus minimizing distortion of the RF envelope. An alternativeconfiguration, which displaces the mid-plane of the track width definedby the head 24 slightly above the neutral plane 16b, also produced asymmetric deflection curve and is shown as the -0.0017 offset curve. Insuch a configuration, the amount of distortion produced is comparable tothe zero (0) offset curve, but a slight improvement of the RF envelopemay be produced. Accordingly it is desirable to achieve the alignment ofthe mid-plane 25 of the track width of the head 24 with the horizontalneutral plane 16b of the member 16. Moreover the net effect achieves, inthe embodiments of FIG. 9A through 9E, an improved head tip penetrationprofile resulting in an improved RF output.

Referring to FIG. 7, the servo circuit 66 for maintaining a videoreproduce head 24 in the optimum transducing relationship with respectto a track 69 extending obliquely across the tape 68 is shown. A ditheroscillator 74 generates a sinusoidally varying signal at a fixedfrequency f_(D). To avoid harmful signal interferences with the recordedvideo signal reproduced by the head 24, the dither oscillator 74 isoperated to provide a pure sinusoidally varying signal at thefundamental frequency f_(D) preferably having less than 1% higher orderharmonic content. The output of oscillator 74 is fed to one input 75a ofa summing circuit 75 where it is added to a low rate or DC errorcorrection signal, present at an input 75b. The output of summingcircuit 75 is amplified by a drive amplifier 76 and the amplified signalis coupled to an inner loop 77 to drive the head 24. The oscillatordrive signal excites the coil element 30 to impart a small peak-to-peak(preferably 10% to 15% of the width of track 69) oscillatory motion(dither) to the head 24 to cause the head to move laterally to the track69 alternately between limits as it scans the track to reproduce therecorded signal. Thus, the drive amplifier 76 is arranged to provide anoscillatory drive signal that causes the head 24 to oscillate or ditherlaterally to each track and about the head's home position as it followsthe track 69.

The oscillatory motion imparted to the head 24 causes an amplitudemodulation of the reproduced signal, which, when recording video orother such high frequency signals, is in the form of an RF envelope offrequency modulated carrier. Because the magnitude of amplitudedeviations in the modulation of the RF envelope are used to maintain thehead in the desired transducing position with respect to the track 69,the precision with which such position is maintained is dependent uponthe sensitivity of the servo drive circuit 66 and how free thereproduced RF envelope is from spurious modulations.

Dithering of the head 24 causes an amplitude modulation of thereproduced RF envelope. If the head 24 is located at the center of thetrack 69, only even harmonic components of the dither signal areproduced by the action of the head 24, because the average head positionis at track center and the envelope variation caused by ditheringappears as a symmetrical function The amplitude of the RF envelopereproduced from the tape 68 is maximum at track center. As the head 24moves to either side of track center, the amplitude of the reproduced RFenvelope decreases by the same amount. The fundamental of the dithersignal is, thereby, balanced out and does not appear as RF envelopemodulation. Therefore, dithering the head 24 laterally to the track 69introduces amplitude deviations in the RF envelope only at twice thedither frequency, f_(D).

On the other hand, if the head 24 is located slightly off the center ofthe track 69 to either side, the reproduced RF envelope amplitudevariation will no longer be symmetrical because head 24 excursions toone side of the track 69 will produce a different RF envelope amplitudedecrease then produced by an excursion towards the opposite side. Hence,the maximum to minimum envelope amplitude variation occurs once for eachcycle of the dither signal, or at the dither frequency, f_(D) with theorder of occurrence of the maximum and minimum points depending upon theside of track center to which the head 24 is offset. The fundamental ofthe dither frequency is no longer balanced out and the reproduced RFenvelope variations will exhibit a fundamental component of the ditherfrequency, with the phase of the fundamental component for an offset toone side of the center of the track 69 180° out of phase with respect tothat for an offset to the other side of track center. Detection of theorder of occurrence of the maximum and minimum points, hence phase ofthe envelope amplitude variations, provides information definitive ofthe direction the head 24 is offset from the center of track 69 anddetection of the envelope amplitude variation provides informationdefinitive of the amount of offset, or a track error signal.

To obtain this head position information, the modulated RF envelopesignal reproduced by the head 24 is coupled to detection circuitryprovided by an outer loop 78 of the servo circuit 66. To an extent, thetracking error signal which varies the amplitude of the reproduced RFenvelope is exhibited as a double-side-band, suppressed carrier (DSB/SC)modulation of the detector fundamental frequency. Therefore, to recoverthe tracking error signal, the reproduced signal output from the head 24is coupled for processing by a simple amplitude modulation RF envelopedetector 79, which is constructed to recover the dither signalfundamental and its sidebands. The output signal from envelope detector79 is merely a rectified version of the reproduced signal, containingthe fundamental and sideband components of the dither frequency, f_(D).The output of the envelope detector 79 is connected to the signal input80a of a second detector 80, which is a synchronous amplitude modulationdetector.

Sync detector 80 is of conventional design of the kind which operates onthe principle of coherently detecting the amplitude and polarity of anunknown input signal with reference to the phase of a reference signalof the same frequency. Such detectors provide a rectified output havingthe amplitude of the unknown input signal and being positive when thetwo signals are in phase and negative when the two signals are 180degrees out of phase The reference input 80b of the detector 80 adjuststhe reference dither frequency provided by oscillator 74 to be at theproper 0° or 180° with respect to the fundamental dither frequencycomponent present in the input to the sync detector 80. Since the signalpresent at the input 80b of sync detector 80 will have a component atthe fundamental dither frequency, f_(D), whenever an error occurs inhead track position, sync detector 80 will provide at its output 80c, atrack error signal representative of the head track position error. Theamplitude of the error signal is proportional to the amount that thebias position of head 24 is displaced from track center. The polarity ofthe track error signal is indicative of the direction of headdisplacement from track center.

This compensated track error signal corresponds to the low rate or DCerror in the position of the head 24 relative to the track 69. The lowrate error signal is applied to the summing circuit 75 where it issummed with the dither frequency output from the oscillator 74. Thecomposite signal resulting therefrom is fed from the output of thesumming circuit 75 to the drive amplifier 76 which applies the compositeerror signal to a summing circuit 82 of the inner loop 77.

The inner loop 77 of the servo circuit 66 is a closed loop servo thatprovides a transfer function in which a one volt input to the summingcircuit 82 equals 4 mils displacement at the head 24. Photocells 59 and60 are disposed opposite the LED 58, with the window 46 of the headsupport member 14 disposed therebetween. At a centered position of thehead 24, the photocells 59, 60 are so disposed opposite the LED 58 thatthe amount of light cast on photocells 59, 60 through the window 46 isequal for both photocells 59, 60, resulting in a minimum (zero) feedbacksignal being input to the summing circuit 82 from the inner loop 77.

From the inner loop 77, the pair of photocells 59, 60 provide respectiveinputs to a difference amplifier 83, each input proportional to theamount of light cast on a respective photocell 59 or 60, the inputs tothe difference amplifier 83 generating a position sensitive differentialoutput which is applied as a feedback signal to the summing circuit 82to modify the error signal from the amplifier 76. The positioncompensated output of the summing circuit 82 is applied to a coil driver84, which supplies a position signal input to the coil 30 to drive thehead 24 to a positional equivalent of the signal output of the summingcircuit 82. An output 85 of the coil 30 is connected to ground.

The magnetic head assembly of the present invention has been describedin connection with the tracking of a tape track on a magnetic tape usedin conjunction with a video recorder, the specific environment for whichit was designed and therefore considered to be the "best mode" of theinvention.

However, it should be recognized that such an assembly can havesubstantially wider use than the described preferred embodiment and suchassembly is not limited to the specific structure of the preferredembodiment. The appended claims are intended to set forth the breadthand scope of the invention described herein.

What is claimed is:
 1. A magnetic head assembly for effectingdisplacement of a magnetic head transversely of a track recorded on amagnetic tape disposed on a rotatable drum, said assembly including amagnetic head, a base mounted on the drum, and head mounting apparatusextending from the base for mounting the head, said head mountingapparatus comprising:an elongated rigid head support member, said memberbeing wedge-shaped over its entire length; a flexure member connectingone end of the support member to the base, said flexure member beingrelatively short as compared to the support member; and a drive assemblymounted on said base and said support member for driving the supportmember for rapidly positioning the head from a first position to asecond and successive positions relative to the track on the tape, thesupport member being sufficiently rigid to reduce undesirable resonancestherein under repetitive loading conditions and cooperative with theflexure member to effect the rapid, head positioning relative to thetrack in response to the drive assembly.
 2. A magnetic head assembly asclaimed in claim 1 wherein head support member has one end connected tothe flexure member with the end of the support member opposite from saidone end defining with said one end a neutral plane of the support memberand wherein the flexure member has a mid-plane coextensive with theneutral plane of said support member, said opposite end of the supportmember being configured to support the head, said head defining a trackwidth with a mid-plane of the head being mutually aligned with theneutral plane of the support member.
 3. A magnetic head assembly asclaimed in claim 2 wherein the opposite of the end of the support memberis tilted away from the tape, with said head engaging the opposite endof said support member so as to align the mid-plane of the head with theneutral plane of the support member.
 4. A magnetic head assembly asclaimed in claim 2 wherein the opposite end of the support member istilted toward the tape, with said flexure member engaging the oppositeend of said support member so as to align the mid-plane of the head withthe neutral plane of the support member.
 5. A magnetic head assembly asclaimed in claim 2 wherein a notch is provided in the opposite end ofthe support member, with the head received in the notch and themid-plane of the head in alignment with the neutral plane of the supportmember.
 6. A magnetic head assembly as claimed in claim 2 wherein atransducer support plate is mounted at the opposite end of the saidsupport member, with the head mounted on the support plate, said supportplate being disposed sufficiently below the neutral plane of the supportmember so as to align the mid-plane of the head with the neutral planeof the support member.
 7. A magnetic head assembly as claimed in claim 2wherein in the head has a notch and the opposite end of the supportmember engages the notch of the head for mounting the head on thesupport member, the head being mounted on the support member so as toalign the mid-plane of the head with the neutral plane of the supportmember.
 8. A magnetic head assembly for effecting displacement of amagnetic head transversely of a track recorded on a magnetic tapedisposed on a rotatable drum, said assembly including a magnetic head, abase mounted on the drum, and head mounting apparatus extending from thebase for mounting the head, said head mounting apparatus comprising:anelongated rigid head support member, said member being wedge-shaped overits entire length and having a bottom wall and opposed laterally spacedside walls connected thereto and at least one laterally extending crossmember connected to the side walls to form an open rigid structure, apair of hinges extending from the end of said support member proximateto the base, said hinges being relatively short compared to the supportmember and connecting the latter to the base, and a drive assemblymounted on said base and said support member for driving the supportmember and for rapidly positioning the head from a first position to asecond and successive head positions which follow the track on the tape,the support member being sufficiently rigid to reduce undesirableresonances therein under repetitive loading conditions and cooperativewith the hinges to effect rapid, repetitive and controlled changes insaid head positions in response to the drive assembly.
 9. A magnetichead assembly as claimed in claim 8 wherein the bottom wall and eachside wall converge from maximum dimensions proximate to the base tominimum dimensions at the head to form a truncated generally triangularshape whereby to maximize the rigidity of the member while reducing itsweight, to achieve an optimum strength-weight ratio for the supportmember.
 10. A magnetic head assembly as claimed in claim 9 wherein thebottom and side walls have openings provided therein, to reduce theweight of the support member without sacrificing its rigidity, byproducing a lattice-type beam structure.
 11. A magnetic head assembly asclaimed in claim 10, wherein the cross member is disposed generallyperpendicular to the bottom wall and has a window opening therein.
 12. Amagnetic head assembly for effecting displacement of a magnetic headtransversely of a track recorded on a magnetic tape disposed on arotatable drum, said assembly including a magnetic head, a base mountedon the drum, and apparatus extending from the base for mounting thehead, said head mounting apparatus comprising:an elongated rigid supportmember having opposed side walls, said member being wedge-shaped overits entire length; a flexure member connecting one end of the supportmember to the base and being relatively short as compared to the supportmember, a drive assembly mounted on said base and said support memberfor driving the support member and rapidly positioning the head from afirst position to a second and successive head positions which followthe tracks on the tape, the support member being sufficiently rigid toreduce undesirable resonances therein under repetitive loadingconditions and cooperative with the flexure member to effect rapid,repetitive and controlled changes in said head positions in response tothe drive assembly; and position sensing apparatus disposed on the baserelative to the head for sensing the position of the head relative tothe track, the drive assembly and the position sensing apparatus beingcooperative to effect said rapid, repetitive and controlled headpositions relative to the track, said position sensing apparatusincluding: a cross member extending transversely of the support memberand connected to the side walls thereof; a window opening in the crossmember; support structure overlying the cross member and secured to thebase; a radiant energy-producing element mounted in the supportstructure and disposed on one side of the window opening; and at leastone photo-sensitive element mounted in the support structure anddisposed on the side of the window opening opposite the light producingelement, with the amount of light cast on the photo-sensitive elementthrough the window opening being proportional to the positional input tothe drive assembly.
 13. A magnetic head assembly for effectingdisplacement of a magnetic head transversely of a track recorded on amagnetic tape disposed on a rotatable drum, said assembly including amagnetic head, a base mounted on the drum, and head mounting apparatusextending from the base for mounting the head, said head mountingapparatus comprising:an elongated rigid wedge-shaped head supportmember; a flexure member extending from the support member to the baseto secure the support member to the base, said flexure member beingrelatively short as compared to the support member; a drive assemblymounted on the support member and on the base for rapidly andrepetitively driving the head; and position sensing apparatus forsensing the position of the head relative to the track, the driveassembly and the position apparatus cooperative to effect rapid andprecise movements of the head through successive head positions relativeto the track.
 14. A magnetic head assembly for effecting displacement ofa magnetic head transversely of a track recorded on a magnetic tapedisposed on a drum, said assembly induding a magnetic head, a basemounted on the drum, and head mounting apparatus extending from the basefor mounting the head, said head mounting apparatus comprising:a headsupport member including an elongated structure having a bottom wall anda pair of side walls connected to and projecting perpendicularly fromthe bottom wall, a pair of hinges connected to and extending fromrespective side walls and at least one cross member joining the sidewalls to form a generally wedge-shaped support member; said hinges beingrelatively short as compared to the support member and being connectedto the base to secure the support member thereto; and a motor driveassembly induding a voice coil motor support spaced from the base on thesupport member and proximate to the head, a voice coil motor retained inthe motor support, and a complementary coil element disposed on the headsupport member in alignment with the voice coil motor for driving thehead support member for rapidly positioning the head from a firstposition to a second and successive head positions relative to thetrack, the head support member being cooperative with the hinges toeffect rapid, repetitive and controlled changes in the head position inresponse to the drive assembly.
 15. A position control system for amagnetic head assembly of a magnetic recorder for effecting displacementof a magnetic head transversely of a track recorded on a magnetic tapedisposed on a rotatable drum, said assembly including a magnetic head, abase mounted on the drum, and head mounting apparatus extending from thebase for mounting the head, said position control system comprising:anelongated rigid wedge-shaped head support member; a flexure membersubstantially shorter than the support member and connected to andextending between the support member and the base for securing thesupport member to the base; a drive assembly mounted on the head supportmember and the base for rapidly and repetitively driving the head from afirst to second and successive positions on the tape; and positionsensing apparatus for sensing the position of the head relative to thetrack including position control circuitry effecting the position of thehead, the head support member being sufficiently rigid to reduceundesirable resonances in the member under repetitive loading conditionsand being cooperative with the flexure member to effect rapid,repetitive and controlled changes in head position produced by the driveassembly and cooperative with the position sensing apparatus to effectsaid rapid, repetitive and controlled head position changes relative tothe track.
 16. A magnetic head mounting apparatus for effectingdisplacement of a magnetic head transversely of a track recorded on amagnetic tape disposed on a rotatable drum, said apparatus including abase and a transducer head defining the track, said apparatuscomprising:an elongated rigid head support member having a first end andextending therefrom to provide a mounting surface for the head at asecond end opposite from the first end, a hinge connecting the first endof the support member to the base, said hinge being relatively shortrelative to the support member, said second end of the support memberdefining a neutral plane of the support member coextensive with amid-plane of the hinge, said second end of the support member beingconfigured to support the head with a mid-plane of the head mutuallyaligned with the neutral plane of the support member, and a driveassembly for rapidly effecting the transverse displacement of thesupport member and the head relative to the track.